Recently, the field of semiconductors, electronics and display devices are rapidly developing. In the field, synthetic resins or synthetic fibers are increasingly used, leading to a troublesome problem of static electricity to be settled. Generally, in the field of release films whose main purpose is to protect adhesive layers, more and more resins or fibers have been used and require antistatic performance for the use. Conventionally, adhesive layers have been made antistatic in order to settle the problem of contamination due to static electricity occurring when a release film is separated from an adhesive layer. However, if the adhesive layer is made antistatic, it does not fully exhibit antistatic performance since antistatic agents are not well compatible with adhesive. Therefore, release layers have been made antistatic, in addition to adhesive layers in many cases. Release property as a physical property required in a release film for the field of precision materials requires a proper peeling force depending on types and use of adhesive, high residual adhesiveness for not lowering adhesiveness by a release layer being transferred to an adhesive layer, solvent resistance that release layers are not peeled off by organic solvent of solvent type adhesive, high light transmission if release films are for optical use, etc.
Conventional antistatic technologies include internally adding anion compounds such as organic sulfonate and organic phosphate, depositing metallic compounds, coating with conductive inorganic particles, coating with low molecular anion or cation compounds, coating with conductive polymers, etc.
A known conventional method of producing antistatic release films with the aforementioned antistatic technologies is to contain metals, e.g., lithium, copper, magnesium, calcium, iron, cobalt or nickel, etc., in silicone compositions (see U.S. Pat. No. 4,764,565). The aforementioned method, however, is not cost effective and also has a limit in achieving antistatic performance: with the method, forming a uniformly coated layer for optical use is interrupted.
If the antistatic composition is of conductive polymers, ion-type polymers, etc., it interrupts curing of silicone release coating compositions, and it is hard to form a release coated layer. Close adhesion between an antistatic layer and a silicone layer is also deteriorated, so that silicone is transferred to adversely affect the function of adhesive. Therefore, in case of a conventional antistatic release film, both of the antistatic performance and the release property can be implemented by applying antistatic compositions on a substrate and drying the film and then applying release coating compositions, or by first applying antistatic compositions on one side of a substrate and then applying release compositions on the other side of the substrate. However, since such a method of forming a conventional antistatic release film requires a coating and drying process to be carried out at least twice, a lot of processing time and cost is needed.